Inner-Outer Member Combination
Various devices presently utilize inner members that are slidable within the confines of outer members (also referred to as “inner-outer member combination”). An inner-outer member combination allows a user to adjust a device's dimension. For example, some tow bars used for towing vehicles have legs that utilize the inner-outer member combination so that they can easily be stored when not in use. Camera tripods also utilize the inner-outer member combination so that they can be stored in a non-bulky manner.
Other devices that utilize the inner-outer member combination include: cleaning poles that allow users to extend the poles to reach a desired height and construction devices that extend to a certain height to transport and allow a person to work on an elevated area, such as billboards. The inner and outer members of these devices may have the same shape, but vary in diameter—that is, telescopic.
Locking Mechanism for Telescoping Legs
Telescoping legs are used in cleaning or agricultural tools (as disclosed in U.S. Pat. No. 5,154,449), legs of common camera tripods (as disclosed in U.S. Pat. Nos. 4,029,279 and 4,761,092), and musical instrument support (as disclosed in U.S. Pat. No. 4,430,017). All of these telescoping legs have a locking mechanism that stops the inner bar from sliding within the confines of the outer bar.
U.S. Pat. No. 5,154,449 discloses a lock for telescoping legs. The lock has a cylindrical clamp, a movable block, and an eccentric shield. The cylindrical clamp is actuated by pivoting the eccentric shield, which causes the shield to pinch the clamp to secure the outer tube and to press the movable block against the outer tube. See also U.S. Pat. No. 4,761,092.
U.S. Pat. No. 4,029,279 discloses another lock for telescoping tubular legs. The lock has a camming lever that engages an inner channel section through a window formed in the outer channel section, thereby locking the inner and outer members. See also U.S. Pat. No. 4,430,017.
One problem with the locks described above is that they are friction-based locks. Friction-based locks rely on friction to prevent an inner member from sliding within the confines of an outer member. However, friction may be overcome by a strong force. Thus, friction-based locks may only be appropriate for limited applications, such as when telescoping legs are used to support lightweight objects or when telescoping legs are not subjected to strong forces. Friction-based locks are also disclosed in U.S. Pat. Nos. 4,029,279, 4,761,092, and 4,430,017.
Tow Bars
Tow bars are devices used for enabling a carrier to tow another carrier. Tow bars are commonly used for enabling a recreational vehicle (an “RV”) to tow a car. Tow bars typically have a pair of legs attached to a leg coupler. The leg coupler attaches to a hitch or a ball mount of the towing vehicle. The other end of the tow bar legs attaches to the vehicle being towed.
A sample tow bar is disclosed in U.S. Pat. No. 5,382,042 ('042 reference), entitled “Towing Device Support.” The tow bar of the '042 reference has a cylindrical inner member that moves in two directions within a cylindrical outer member. In one embodiment, the cylindrical outer member has a latch attached to one end of the cylindrical outer member. The latch has a handle on one end and a stopping potion and a tooth on another end. The tooth is adapted to abut a dimple on the inner bar. The dimple is substantially a triangular shaped indentation on the inner bar. The tooth of the latch is adapted to go inside the indentation and abut the bottom of the dimple's triangle thereby preventing the inner bar from sliding toward the bottom triangle side. However, the inner member can still move in the opposite direction because the tooth can disengage from the dimple by sliding toward the crest of the dimple's triangle, as there is no structure designed to stop the tooth at the crest. When the tow bar is being used, the inner member's movement within the confines of the outer member exposes the tow bar to damage and possibly to the detachment of a vehicle being towed from the towing vehicle.
The '042 reference also discloses an embodiment where the inner and outer members are secured by a pin attached on the outer member. The pin is adapted to insert through an opening defined by the inner member, thereby interlocking the inner and outer members. The problem with using a pin as a locking mechanism is that it might break, especially when towing a heavy load.
Another problem with the '042 reference is that high friction builds in between the pin and the opening or in between the latch and the dimple when a vehicle is being towed. Because of this high friction, a user may not be able to remove the pin from the hole or the latch from the dimple when the user wants to slide the inner member within the outer member to, for example, store the tow bar. This situation is commonly known in the art as being in a “bind.” To get out of the bind, the user would have to re-board the towing vehicle and drive the towing vehicle back and forth until the friction is relieved off the pin. Driving the towing vehicle back and forth may not even remove the bind, especially when the towing vehicle and the vehicle being towed are on an uphill surface.
Another tow bar is disclosed in U.S. Pat. No. 5,957,477 ('477 reference). The '477 reference has two leg members that are attached by a slideable collar, which moves between a locked and an unlocked position. Each leg member has an inner member that has grooves and an outer member that has catches. The catches attach to the grooves when the collar is in a locked position, thereby interlocking both members. Like the tow bar previously described, the catches might disengage from the grooves, especially when towing a heavy load.
The '477 reference is also susceptible to “binding.” In fact, the '477 reference provides a separate release tool for a user to remove an inner bar that is “bound” with the outer bar. Thus, a tow bar that has little or no tendency to “bind” is desired. Additionally, a tow bar that has an integrated tool for releasing “bound” members is also desired because separate tools are easy to lose and are complicated to use.